Planetary gear

ABSTRACT

A planetary transmission which has a drive shaft, an axial bearing, an internal gear, an axially displaceable sliding collar and a lubrication circuit and an output shaft which is mounted the transmission housing by an external bearing and an internal bearing. The housing is provided with an oil intake ( 13 ) which is connected to an oil line ( 16 ) with the external bearing ( 5 ) of the output shaft, which is linked by an oil feeding circuit with the axial bearing ( 9 ) of the output shaft. The axial bearing ( 9 ) is connected with an interior gear bearing by an interior gear ( 17 ), the interior gear ( 17 ) is encapsulated through a wall section ( 18 ). An oil discharge ( 14 ) is connected with an oil pump located outside the planetary transmission which, on the other hand, is connected with the oil intake ( 13 ).

This application is a national stage of PCT/EP2004/010885 filed Sep. 29,2004 which claims priority from German Application Serial Nos. 103 48757.3 filed Oct. 21, 2003, 103 48 755.7 filed Oct. 21, 2003, 10 2004 003684.5 filed Jan. 24, 2004 and 10 2004 003 685.3 filed Jan. 24, 2004.

FIELD OF THE INVENTION

The present invention refers to a planetary transmission, in particularfor machine tools.

BACKGROUND OF THE INVENTION

Such planetary transmissions, mostly built from single- or multiple-stage planetary transmissions, are basically implemented in machinetools, as well as in lathes, milling machines and machining centers. Theselectable planetary transmission increases the service scope of themain spindle motors, as well as the flexibility of the machine tool forprocessing the different work materials through increasing high torquesor high speeds. For example, two transmission stages may be built in,while on one hand, the drive shaft which is connected to a sun gear withan internal gear and on the other, the internal gear can be coupled tothe housing. A planetary carrier is connected to the output shaft.

In DE A 199 17 673 of the applicant, there is such a two-stage planetarytransmission, with a drive shaft and an output shaft which are mountedin the housing over roller bearings. The drive shaft is connected to asun gear which engages with the planetary gears, which are mounted overbearings on planetary bolts in a planetary carrier, which is connectedover a positive-fit connection with the output shaft. The planetarygears are combed with an internal gear, which is mounted over the rollerbearings in the housing or in the rotating planetary carrier andpositively fit with a hub connection. The hub is torque-proof connectedover an external gearing with the first part of the sliding collar.

A roller bearing is located over the sliding collar. The external partis axially displaceable in the housing, running over bearing bolts,whereby the axial displacement of the external part is carried over theroller bearings.

The sliding collar displacement takes place by means of a switchingdevice, which is actuated by a solenoid or by a motorized switching unitwhose armature is connected with the sliding collar.

This kind of planetary transmission has multiple rotating elements and,consequently, many bearings which are lubricated with the appropriateoil. Most of the traditional planetary transmissions for machine toolsuse splash lubrication, which has the disadvantage that it may betainted with high mix losses and that the maximum possible rotationalspeed of the internal gear is limited by the internal gear bearings asthey get warm, as the absorbed heating cannot be released. It ispossible to cool the splash lubrication oil with circulatorylubrication, without avoiding the mix losses.

Further planetary transmissions are built with circulatory lubricationand oil cooling. High mix losses are shown also in these cases, on whichthe target maximum rotational speed of the interior gear is onlypossible conditionally. Under very high rotational speeds, the oil fromthe central part will be shot by the centrifugal force towards thehousing, leaving the center of the transmission with a low oil levelduring the operation, generating frictional corrosion.

Operation of a planetary transmission with oil spray lubrication hasalso been tried. This is however not applicable for planetarytransmissions, as the oil spray cannot reach the center of thetransmission because of the strong ventilation effect caused by the highrotational speed of the interior gear, which means that the sun gear isnot lubricated. Therefore the axial bearings will be insufficientlylubricated and frictional corrosion may even be generated.

SUMMARY OF THE INVENTION

The purpose of the present invention is to create a planetarytransmission with a lubrication circuit that is reliable under the highrotational speed of the interior gear and at the same time under lowtemperatures, so that no more frictional corrosion is generated.

The invention proceeds from a planetary transmission, in particular formachine tools, that has a drive shaft connected to a sun gear; an outputshaft that is connected to a planetary carrier and that is mounted overthe transmission housing with a first external bearing and with a secondinternal bearing, where both bearings are separated from each other bymeans of a piston ring; an axial bearing; an interior gear which islocated over the interior gear bearing in the transmission housing; anaxially displaceable sliding collar which is mounted over sliding collarbearings; and a transmission lubrication circuit with an oil pump.

According to the invention, it is planned that the oil pump be locatedoutside the transmission, that the housing has an oil intake, that thisoil intake is connected to an oil line with the first external bearingof the output shaft, that the bushings have a small borehole forconnecting the piston ring, that the first external bearing is connectedto an oil supply circuit with the axial bearing, that the axial bearingis connected over a cavity with the interior gear bearing, where thecavity is encapsulated through a wall section for the oil discharge holein the transmission housing, and that the oil discharge is connected tothe oil pump by an oil line.

With the invention based oil circuit application, it will be possible tohandle higher rotational speeds of the interior gear based on lowertemperatures, and no more frictional corrosion will be produced. It maybe further possible to achieve a dry lubrication system, which meansthat no oil level will be necessary in the planetary transmission, bywhich also no mix losses and no temperature increase will occur, incomparison with the traditional planetary transmissions that showdifferent oil levels that depend on the rotation direction and that havedetrimental effects on the oil temperature.

The invention is explained in further detail in the only FIGURE, inwhich a section of a two-stage planetary transmission is shown, inparticular for a machine tool, on which the proposed lubrication circuitcan be seen.

BRIEF DESCRIPTION OF THE DRAWINGS

Two-stage planetary transmissions for machine tools are well known byspecialists, therefore only the description required for understandingthe parts of the proposed invention follows.

DETAILED DESCRIPTION OF THE INVENTION

The drive shaft of the transmission is identified with number 1. The sungear to which it is connected is identified with number 2, while theoutput shaft is identified with number 3 and the planetary carrier towhich they are connected with number 4. The oil intake is identifiedwith number 13, the application example close to the switchgear isidentified with number 19, which is intended for the sliding collar 11in the bearings or in the transmission housing. This oil intake isconnected with an oil pump (that is not shown) outside of thetransmission, and with an oil line 16, which is built into the wall ofthe transmission housing with the first external bearing 5 of the driveshaft 3. The first external bearing 5 is sealed off from the secondinternal bearing 6 by a piston ring 8, whereby this piston ring 8 isprovided with an opening. This opening can either be the small borehole15 of the piston ring that penetrates the internal or external bushingparallel to the drive shaft axle, or a narrow gap between piston ring 8and the external bushing, so that a small oil quantity is applied to thesecond internal bearing 6.

The first external bearing 5 is connected with the axial bearing 9 overtwo parallel oil lines 16′, 16″ in the longitudinal axle of the outputshaft, which in order to prevent unbalancing are placed over thelongitudinal axle symmetrical levels of the output shaft. Either asingle oil line or more than two oil lines can be applied.

Both of these oil lines 16′ and 16″ remain perpendicular to the outputshaft over the longitudinal axle penetrating borehole 20 connection. Oilfrom the first external bearing 6 to the axial bearing 9 flows throughthis oil circuit.

The oil flows to the output shaft center, where it arrives afterflooding axial bearing 9 due to the rotational force in the direction ofthe housing inner wall. A cavity 17 runs through the closed bearinghousing wall section 18, through which oil will flow to interior gearbearing 11, which will then be optimally lubricated and cooled, allowingthe rotational speed to be increased. In the traditional planetarytransmissions, the maximum rotational speed of the transmission islimited by the top rotational speed of the interior gear.

The closed bearing housing on wall section 18 is encapsulated due to therapidly turning interior gear 11, whereby the interior gear oiladulteration is prevented or at least significantly reduced, and arotation direction depending oil level is also avoided.

The interior gear bearing 11 is not connected with the sliding collarbearing 12 of the sliding collar 26, as this sliding collar bearing,which due to its small overall size is not critical for the rotationalspeed and in addition must not absorb any axial and/or radial forces, itcan be lubricated with an oil spray.

Provided that the planetary transmission has an adapter plate 21 betweenthe drive shaft and the transmission, it will then have its own oilintake 23, on which an oil line 22 is attached for lubricating theassociated bearing 24. This oil line 22 is provided with a dischargeborehole 25, so that in case a high oil quantity circulates through it,there is also high oil pressure in line 22.

In one (not shown) application example, instead of the oil intake 13close to switchgear 19 there is a centered axial borehole in drive shaft3, so that oil can flow through this centered borehole to oil lines 16′,16″ and 20. The oil intake 13 may also serve for feeding.

It should be stressed that it is also possible to deploy an oil circuitin the opposite direction, which means that the above-described oildischarge 14 can be the oil intake, and the above described oil intake13 can become the oil discharge.

The continuous flow over the planetary transmission provides excellentlubrication, at the same time excellent oil cooling, and prevents theformation of frictional corrosion.

The dry lubrication system according to the invention eliminates theneed for an oil level together with adulteration and the until nowunavoidable temperature increase. The selective lubrication of theindividual machine components leads at the same time to a significantrotational speed increase of the internal gear by reducing thefrictional corrosion. The encapsulation through wall section 18contributes significantly to these benefits.

Reference Signs

-   1 Drive shaft-   2 Sun gear-   3 Output shaft-   4 Planetary carrier-   5 External gear-   6 Interior gear-   7 Housing-   8 Piston ring-   9 Axial bearing-   10 Interior gear-   11 Interior gear bearing-   12 Sliding collar bearing-   13 Oil intake-   13′ Oil intake-   14 Oil discharge-   15 Borehole-   16 Oil line-   16′ Oil line-   16″ Oil line-   17 Cavity-   18 Wall section-   19 Switchgear-   20 Oil line-   21 Adapter plate-   22 Oil line-   23 Oil intake-   24 Bearing-   25 Discharge borehole-   26 Sliding collar

1. A planetary transmission for machine tools, the planetarytransmission comprising: a drive shaft that is connected to a sun gear;an output shaft connected to a planetary carrier and mounted over atransmission housing by an external bearing and an internal bearing,both of the external bearing and the internal bearing being separatedfrom one another by a piston ring; an axial bearing; an interior gearwhich rotates over an interior gear bearing and is located in thetransmission housing, an axially displaceable sliding collar; and alubrication circuit in the transmission; the housing being provided withan oil intake (13) that is connected to an oil pump located outside thetransmission, the oil intake (13) supplies an oil flow over an oil line(16) to the external bearing (5) of the output shaft (3), the pistonring (8) is located between the external bearing (5) and the internalbearing (6), the oil intake (13) serves as an oil passage, in which theexternal bearing (5) is connected through an oil feeding circuit withthe axial bearing (9), and the axial bearing (9) is connected with acavity (17) in the interior gear bearing (11), the cavity (17) isencapsulated through a wall section (18) of the transmission housing toan existing oil discharge (14).
 2. The planetary transmission accordingto claim 1, wherein the oil feeding circuit, between the externalbearing (5) and the axial bearing (9), comprises of at least one line(16′, 16″) that run parallel in a symmetric level through a longitudinalaxis of the output shaft (3).
 3. The planetary transmission according toclaim 1, wherein the oil intake (13) is provided in at least one of theinternal bearing, the external bearing and the axial bearing and in thetransmission housing.
 4. The planetary transmission according to claim1, wherein the oil intake is located in a centered borehole in theoutput shaft (3).
 5. The planetary transmission according to claim 1,wherein a discharge of the piston ring (8), implemented in the pistonring (8), crosses parallel to a longitudinal axis of the output shaft(3), without any borehole (15) in either one of an external bushing oran internal bushing.
 6. The planetary transmission according to claim 1,wherein a piston ring (8) discharge is a narrow gap between the pistonring (8) and an external bushing.
 7. The planetary transmissionaccording to claim 1, wherein when an adapter plate (21) is placedbetween the drive shaft and the planetary transmission, the plate (21)is provided with an oil intake (23) and with an oil line (22) so thatthe plate (21) is connected to a discharge borehole (25) with thetransmission.
 8. The planetary transmission according to claim 1,wherein the oil intake becomes the oil discharge and the oil dischargebecomes the oil intake.
 9. The planetary transmission according to claim1, wherein the oil feeding circuit, between the external bearing (5) andthe axial bearing (9), comprises of a plurality of lines (16′, 16″) thatrun parallel in a symmetric level through a longitudinal axis of theoutput shaft (3), the plurality of lines (16′, 16″) are connectedperpendicularly to each other over the longitudinal axle of the outputshaft (3) and to a penetrating oil line (20).